Real World Impact Test

A few weeks ago Selemat, a McCurdy and Rhodes 66, a big sister to our own Morgan’s Cloud, came through Lunenburg, here in Nova Scotia, and I went to visit.

We were sitting in the cockpit chatting over a beer with the owner, crew, and my friend John Clayman, who managed the mega-refit that the boat just came through to restore her to her former glory, when I asked a question:

Anyone know why there is a short piece scarfed into the toe rail on the port side only?

Everyone looked at me blankly, so I told a story:

Some thirty years ago I was the bowman, perched on the pulpit of a 44-foot ketch, calling the line at the start of a race at Antigua Race Week. I had just yelled “clear”, as the gun went, and then I glanced aft at the bigger boats milling around awaiting their start, to see the most incredible scene unfolding.

A huge Fife wooden ketch—I think it was Belle Aventure, although my memory may be faulty on that—was bearing down on Selemat (then called Rebel) with a bone in her teeth and a full on trade wind at her back. A good 80 tons of mass traveling at at least 8 knots—now that’s momentum!

I know it’s a cliché but time really did seem to stand still. To this day, I have a picture in my mind of the helmsman on Rebel holding his hands up toward the onrushing bow towering above him, as if to fend off, before self preservation kicked in and he dived for the cockpit sole as the ketch’s bow buried itself in the side of Rebel, almost exactly amidships, with a crash that must have been audible five miles away.

I have no idea what the forces involved were—I will leave that to the engineers—but they were certainly prodigious. I fully expected Rebel to be cut in half, or at least sink immediately, and the helmsman to be killed.

Not a bit of it. As I remember, Rebel took on no water and only suffered a V-shaped indentation at the point of impact. You can see how the damage was contained by the small size of the piece scarfed in. I’m not sure what happened to the helmsman but I’m sure I would have heard about it if he had been seriously injured.

McCurdy and Rhodes have long had a reputation for “over-specifying” the construction of their boats and the outcome was a tribute to Rebel’s scantlings and super strong aluminum construction.

But that begs the question, how do you define when a boat is strong enough? Normal use, or when shit happens? Sadly, I fear that the former is the criteria with many modern production boats. Something to keep in mind when shopping for a boat to take you and your family cruising, where sooner or later, shit will happen.

By the way, although I make no secret of my personal preference for aluminum, I am not saying, or even implying, that boats can’t be built of other materials to be able to withstand unusual, but all too possible, impacts.

For example, heavily built fiberglass fishing boats are the norm around here in Atlantic Canada and they are regularly subjected to brutal treatment, including shunting ice, without damage.

Comments

Does anyone else have any first hand stories about impacts on voyaging boats and the outcome? If so, please leave a comment.

Further Reading

You can read more about hull materials and impact resistance here and here.

I find your comments on modern production boats fully justified. One of the reasons we went for steel was not because we believe it to be superior to fibreglass, but that fibreglass is not being laid up to what we consider strengths and scantlings fit for purpose…which could involve close encounters with other boats, bergy bits or coral heads. To find this level of construction means shopping in the higher tiers (Swan, Moody, Oyster, etc.) the purchase of which would have meant a further delay in fitting out and pushing off.

Add to that my vicarious experience of seeing a boat-knowledgeable friend shopping for “new-used” production boats (under three years old) and finding core voids, incomplete or missing tabbing, clustered bulkhead holes (making for weak spots) and a general slap-dash air when it comes to fit and finish…and we have not developed a very good opinion about modern production cruisers. Like certain products of Hollywood, they look great in a medium close-up, but in person are too damn thin!

Indeed, but much as I would have preferred a ketch if only we had been able to find one in good condition, I would have happily had a fibreglass boat. We went to steel not just for its own merits, but because we couldn’t find sufficiently well-constructed (in our view for our projected purposes) boats in fibreglass.

We’ve seen very few aluminum boats “live” where we live, although almost every police boat on the Great Lakes is now in locally built alu, as is our club’s new workboat. I’ve liked what I’ve seen, but simply lacked the experience when we were shopping seven years ago to know when I’m looking at high build and finish standards in that material.

I suspect that is the case with fibreglass: it is so dominant a material for under-50 footers that anything else is simply not considered by the typical (non-high-latitudes cruising) buyer.

One caution: if that boat was going to go offshore after that treatment, the owner would want to be very sure that invisible, but still dangerous, damage had not been done to the laminate, particularly at the bow and keel to hull joint. Matt, AAC Technical Correspondent, explains that issue with GRP laminates in this chapter.

Our Van de Stadt Samoa 47, “Billy Ruff’n”, was built in steel in Australia in the early 1990s. In 2006, she went bounding into an underwater boulder field in Alaska at a bit over six knots. We stopped in no more than a boat length. (Yes, the rock was on the chart). My wife was below at the time and ended up on the cabin sole. I was at the wheel and drew blood when my head impacted the dodger frame. Damage to the hull was limited to paint scrapes all over the forward part do the keel and a small 1″ deep dent at the bottom of the leading edge of the keel. No leaks, no cracked welds, just minor body work at the end of the season. If you’re dumb enough to hit a rock, it helps to be in a well built steel boat.

The real damage and most expensive repair was to the rig. The impact and rapid deceleration caused the aluminum mast to flex forward and put small cracks in the leading edges of all four spreaders and several of the sheeve boxes. This we didn’t discover until the end of the season as it never occurred to me to check anything but the hull for damage immediately after the crash. The rig had to come out for a thorough inspection and welding repairs. The rig repairs were 2X the cost of the paint work on the keel.

In addition to a strong hull, a good offshore boat will have a rig that will survive a brief encounter with a hard spot in the ocean.

I also witnessed a ‘T’ – bone collision at the Antigua Race Week in the late seventies when I was a deckie there (time does fly!). The collision was between an Ocean 71 and a Swan 43′ with the Ocean doing the ‘T’-boning. The damage to the Swan was right amidships and not only pushed the topsides in but of course moved all of the interior carpentry along with it.

The point is that GRP cannot be made as strong or integral as a repair due to it’s chemical composition in that GRP layup is a reaction, and old and new GRP does not react, just sticks (Matt I stand to be corrected), but metal, be it steel or aluminium can, by cutting out and replacing the damaged area (so can wood for that matter).

That’s a very good point, having had sever problems with secondary bonding failures on my first boat, I would never trust a fiberglass boat that had had a major repair using polyester resin since there is simply no way that I know of to get a good bond between the old and the new.

Having said that, I was able to solve the problems on the old boat by using epoxy resin to make the repairs, because it will stick properly to a polyester laminate as long as the preparation is done properly.

Like you, I really like the fact that aluminium can be easily repaired to its original strength. One thing though, when welding to older aluminium the surface must be meticulously cleaned since any contaminates left can compromise the integrity of the weld in ways that are impossible to determine, except by x-ray examination.

GRP (fibreglass) repairs are tricky. If you cut out the damaged area, and fill it in with new fibreglass and polyester resin, it will probably fail.

If you cut out the damaged area, cut back the individual layers of fibreglass around it in a “stepped” fashion, scrub it clean with the right solvents, cut new pieces of fibreglass for each of those stepped layers, and laminate it up with epoxy, it can be just as strong as the original hull (or even stronger, if the original build quality was less than great).

The question is “does the repair guy know what he’s doing, and is he using the right products?” rather than a blanket statement of “secondary bonding sucks”.

It’s also quite possible to screw up an aluminum repair. If the guy at the yard grabs a chunk of the wrong alloy and tries to MIG-weld it in with CO2 shielding gas instead of argon, the result will be just as bad as the polyester/fibreglass patch on the GRP boat.

Full-strength repairs are possible in all common hull materials, as long as the person doing the work knows how to do it properly.

Very well put: it’s a lot more about the person doing the repair than it is about the material.

There is one nice thing about metals, and that is that there are recognised industrial welding qualifications and standards that can help the boat owner, to at least some extent, determine whether or not a yard knows what they are doing. Sadly, at least as far as I know, there are no comparable international, or even national standards for people working in composites.

One question: I was able to fix secondary bonding issues on my old boat using epoxy resin, but I was just working on things like bulkhead tabbing and the mast step. Are there any engineering issues in using an epoxy based laminate to repair a large hole in hull laid up with polyester resin? Hard spots caused by different stiffness, for example?

After read this article and some opinion … I have some doubt about strenght fiberglass. I work 2 year to make strong my marieholm26 folkboat for offshore sailing… So is better to Thinking a steel boat bow?
Gab

Hi John,
I saw the article about material, but after looking on your web site any thing I did on my boat seem nothing respect the boat you got.
I will try to prepare my boat for offshore sailing and my choice was for one of the “twenty small boat to take you anywere” a folkboat Marieholm 26. I spent 2 year to prepare it to be strong and safe.
Many works are planned this autumn. This is what I can afford now.. In the future hope in a steel boat!
Ciao from Venice

I think you are doing exactly the right thing: going now in a smaller wholesome boat. I don’t know the Marieholm 26, but many safe and seamanlike voyages have been made in Folkboats. In fact I once met a man from the Netherlands who had sailed safely all over the North Atlantic in one built from fiberglass.

Two years ago I spent the night anchored behind Quito Sueno reef. * The nearest land is about 120 miles downwind in Honduras, and there isn’t a single inch of the reef that isn’t underwater. To get to the face of the reef involves eyeball navigation through about 12 miles of uncharted coral gardens on the lee side. There is no charted pass out the front, although we found one exploring by dingy.

There were three other boats visible, all made of steel –some of them several hundred feet long. Unfortunately they were all pointing bow up at 45 degrees. Spookiest place I have ever been, with the ghosts of dead sailors wandering about at night.

The point of the yarn is that in truly remote areas a hard grounding at the wrong stage of the tide (or where there is no tide) probably means that any deep draft fixed keel boat has found her final resting place regardless or what material it is made of. A fiberglass boat will be ground to pieces in a few hours, while a metal one may maintain its watertight integrity for a day or two, but without outside assistance your chances of saving her are not good.

The only kind of boat that I would re-visit Quito Sueno in is a retractable daggerboard catamaran with kick up rudders or an aluminum integral centerboarder with kick up rudders.

* how I ended up in such a palace is another story. Suffice to say that a certain species of very rich people believe that their money can solve any problem that might come along, which grants them total immunity.

One of my friend Kurt Hughes first certified passenger catamarans is named Sierra Cloud, and has been carrying 50 passengers daily for over 25 years on Lake Tahoe. It was built using his rapid build cylinder mold method which he pioneered as an USCG approved construction technique for passenger vessels. The result is an ultra light skin made from epoxy and 1/8″ door skins. In the case of the 55′ Sierra Cloud the finished hulls are only about 3/8″ thick. The exact opposite of a Dashew or McCurdy & Rhodes aluminum construction.

A few years back a jet ski hit the side going full throttle. It hit so hard that it had to be removed from inside the boat. A little epoxy, some 1×2 fir stringers and a few door skins and the boat was back in service ready for another decade or two. Of course it didn’t sink, because there was no hunk of lead to drag her down. There is something to be said for cheap and repairable.

*for those who are curious, a half hull for a 70′ 150 passenger catamaran was recently laid up in little over 1/2 hour from start to finish using this method.

It sounds fantastic to have hulls that can be built so easily. I wonder however, are these hulls up to the continuous beating they have to take on an ocean passage? And what happens once they are breached out on the ocean?

Wood-composite structures can be remarkably resistant to fatigue; there are ways to build hulls like this (Kurt’s method among them; Lindsay Lord’s strip-planked technique is another) that tolerate a bit of flexing in the wood skins in ordinary use. It’s a bit disconcerting at first to someone used to very rigid structures, but it lasts just fine for many decades.

It’s even possible to build a flexy, yet fatigue-resistant structure in aluminum; the wing of a Boeing 767 bends quite a bit more than the nearly rigid wing of the competing Airbus 330, yet the life expectancy is about the same. (Hard to do that in a boat, though, without Boeing’s engineering resources.)

Fatigue isn’t terribly difficult to allow for, if you consider it carefully at the design stage. Where you tend to see fatigue failures is in something that was assumed to be perfectly rigid, and turns out not to be.

Hi Eric,
20+ years of continuous 300 plus day per year service in ocean conditions in Hawaii is certainly equivalent to many lifetimes of ordinary cruising longevity. Properly engineered even this light and low tech construction can be extremely durable.

What happens to a properly designed catamaran if you hit something and rip the bottom open or have a hose come off a seacock? You move the bedding up to the salon and keep on sailing.

Hum, while I agree that not having ballast to sink you is a benefit of multihulls, I’m not sure it’s really that wonderful. I’m no expert, but most cruising cats will have engines and other items that weigh a lot and will
drive a flooded hull well down into the water, probably nearly awash. I would really doubt that it would be viable to sail a cat with a flooded hull unless it was equipped with a lot of foam buoyancy or a lot of watertight compartments.

Having said that, it would, I think, be a lot more viable to patch the hull and pump it out on a cat, as measured against a monohull which, without watertight bulkheads, will sink pretty quickly with a surprisingly small hole.

Hi John
I agree that MOST cruising catamarans will be difficult at best to try to sail with a flooded hull. That is why I included the qualification “properly designed”! (LOL)
Here is an example of a properly designed 53′ catamaran. (http://www.multihullcentral.com/schionning-g-force-attitude/) Not the expedition catamaran design idea we tossed around earlier, but for somebody with deep pockets it is hard to imagine a better South Pacific island explorer. And living proof that not all catamarans are ugly! It has all the bells and whistles that any millionaire might desire, but could easily loose several hundred pounds if it were built with foam core instead of balsa and had a carbon mast. Even as built and equipped I’d guesstimate that it would still have as much as a foot of bridge deck clearance with both hulls punctured, and thus still be capable of being sailed to port.

The key to having a catamaran that is not just unsinkable, but will retain some functionality is the same high surface area of the two hulls that makes them inherently expensive to build. On my Lightspeed 58 design we used 1″ CoreCell in the hulls— tremendous inherit flotation capability for a 22,000# displacement. On that design we had 11″ underneath the floorboards which could easily have been filled with foam. Now we are starting to describe a boat that could indeed sail long distances at reduced speed after having a hull punctured. Or motor if it has sail drive engines in water & sound tight enclosures.

That must have been an incredible collision to witness. One of the reasons that I have never really been interested in racing is all of the playing chicken that goes on and the collisions. I do my yearly race at the Gloucester Schooner Race and even that has had a few collisions in the past few years.

Unfortunately, how a boat will hold up seems to really depend on the specific design as much as anything else. Unless you spend a lot of time really studying and analyzing the different features yourself, you just have to trust that the designer took care of any potential weaknesses. I have seen 2 pretty spectacular failures of the deck/hull joint due to racing (not voyaging boats) in what I would consider relatively minor collisions with boats that didn’t show obvious signs of previous issues. To me, this highlighted an area of the boat that was much weaker than the rest and my gut reaction is that you don’t want to design an intentional weak point into this type of structure. While I have seen a number of pretty catastrophic failures and instances where I was amazed that there wasn’t one, the sample size is just so small that I consider it meaningless.

It would be interesting to hear what people like Bob Perry, Ed Joy, Ian McCurdy, etc do for analyses on the boats that they design. If it were a car, the design specification would call for the design to withstand specific impact forces at specific locations with only certain amounts of damage. Do they state that the bottom foot of the leading edge of the keel must be able to hit something with the stiffness of concrete with the boat traveling at 6 knots and there be no yielding? Since boats are so low volume, destruction testing them is not feasible but the FEA tools are good enough these days that in the right hands(this is the huge danger), you can do a really good job of predicting how a built to spec structure will fail.

It would be really interesting to look at the boats that come out of charter in a place like the Bahamas where they constantly run aground, often at reasonable speed. I remember getting aboard a charter boat at a dock there and thinking that the motion was strange only to realize that it was aground at its normal berth and even though I waited for high tide, we still pushed sand the whole way out.

All interesting points, as always. I think the key takeaway for most of us is your point that a detailed engineering analysis of an existing boat is really pretty impractical and therefore we need to come at the problem by selecting a boat designed by someone we trust with deep experience with the material the boat is built out of, and then verify that the boat was properly built to the design scantlings.

This is precisely the path I took when I bought “Morgan’s Cloud”.

This is an path that it is easier to follow in metal boats than GRP, since it is easier to check that the scantlings match the design in the former.

When I bought our steel boat, I contacted the original designer who is still in the business. He was kind enough to send me photocopies of three plan views from his files and I was able to grub about with a tape measure inside the hull to see that the “stations” were as designed. There were clearly some differences, most minor, however, between the design and the builder’s execution.

Reviewing these changes and “boatyard design decisions” has given me insight into issues of trim, where the center of effort and center of gravity are likely to be, and other aspects of how a boat that is otherwise a one-off might perform. I feel somewhat lucky that, not being the original owner, I was able to get these documents at all. They’ve been exceptionally useful, and will continue to be so when we load the boat for offshore use.

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